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921.
本文以广东省赤红壤水土流失区为例,综合分析了赤红壤水土流失区发展持续农业的存在问题,在此基础上提出了该区发展持续农业的途径与对策.认为:水土流失区发展持续农业存在的突出问题主要是土壤退化;发展持续农业的根本途径在于走生态农业的道路,建立立体农业生态系统;侵蚀土壤上重建森林植被群落首先要建立先锋群落,然后建立稳定的南亚热带森林植被群落。 相似文献
922.
Influences of Suspended Particles on the Runoff of Pesticides from an Agricultural Field at Askim, SE-Norway 总被引:1,自引:0,他引:1
Q. Wu G. Riise H. Lundekvam J. Mulder L.E. Haugen 《Environmental geochemistry and health》2004,26(2):295-302
Field and laboratory experiments were conducted to study the loss of particles from agricultural fields, and the role of suspended particles in carrying pesticides in surface runoff and drainage water. Propiconazole, a widely used fungicide was applied to experimental fields located at Askim, SE-Norway. Samples from surface runoff and drainage water were collected and analyzed for sediment mass, pesticides, particulate and dissolved organic carbon through a whole year. The surface soil and the runoff material were characterized by its particle size distribution, organic carbon content in size fractions and its ability to bind propiconazole. The results show that (1) particle runoff mostly occurred during the rainfall event shortly after harrowing in autumn. The highest particle concentration observed in the surface runoff water was 4600 mg l–1, and in the drainage water 1130 mg l–1; (2) the erosion of surface soil is size selective. The runoff sediment contained finer particle/aggregates rich in organic matter compared to its original surface soil; (3) the distribution coefficient (K
d) of propiconazole was significantly higher in the runoff sediment than in the parent soil. According to our calculation, particle-bound propiconazole can represent up to 23% of the total amount of propiconazole in a water sample with a sediment concentration of 7600 mg l–1, which will significantly influence the transport behavior of the pesticide. 相似文献
923.
Francesca Gherardi 《Behavioral ecology and sociobiology》2006,59(4):500-510
A study was conducted to determine whether asymmetries in both resource-holding potential (RHP) and resource value (RV) influence
dominance and fighting behavior in the hermit crab Pagurus longicarpus. A total of 120 groups of three crabs were observed for 10 min in four experiments that tested all diverse combinations of
equal/different RHP (i.e. ‘body size’) and equal/different RV (i.e. ‘shell size’ and ‘shell quality’). In a fifth experiment,
dominant and subordinate individuals of the same size category (26 groups) were forced to enter shells of opposite quality
than those previously occupied, and then the behavior of the reconstituted original groups was observed for additional 10 min.
As expected, crabs in lower quality shells were more willing to initiate and to escalate fights. However, their attacks were
directed to any crab of the group, independently of the defender's shell quality, and the fight duration did not vary with
the different value of the resources at stake. This may indicate that P. longicarpus is unable to assess the quality of the shells available in its social environment but bases its tactical decisions during
fights solely on its own resource. This suggestion was confirmed by the change in the fighting behavior of crabs whose shell
quality was experimentally altered. This manipulation induced an overall increase in the intensity of aggression, drastic
modification of crab behavior, and inversion of the hierarchy even though these crabs have had previous experiences of wins/losses
and were familiar to the other members of the group. In this species, large crab size and/or the occupancy of adequate (and
oversized) shells appeared to be the most likely determinant of contest resolution. Individuals seemed to retain a memory
of the previously held resource and behaved accordingly. 相似文献
924.
To maximize reproductive success, reproductive behaviors have to be adjusted to environmental conditions. The breeding habitats
of the threespine stickleback Gasterosteus aculeatus are presently changing in the Baltic Sea due to eutrophication and enhanced growth of filamentous green algae. Earlier studies
show that high algae density reduces mate encounter rate and the intensity of selection on a few sexually selected traits,
but the willingness of males to nest under the new conditions, and their investment into reproduction, have not been investigated.
Here, we investigated the effect that increased algae growth has on nesting behavior of sticklebacks. We allowed males to
build nests in aquaria with either a sparse or a dense vegetation structure and recorded male nest building behavior and nest
characters. Males that nested in dense vegetation showed a longer latency before commencing nest building and also completed
nest building later since there was no difference in time spent building. There was no effect of vegetation cover on nest
characters. These results suggest that males prefer to nest in sparser vegetation, but that they eventually nest in dense
vegetation if more open habitats are not available. This may arise from a negative effect of vegetation on visibility and
mate encounter rate and thus on expected reproductive success. This implies that human-induced changes in the environment
may force sticklebacks to breed in non-preferred habitats. Since the intensity of sexual selection is reduced in these areas,
this could influence the further evolution of the population. 相似文献
925.
A GIS-based vulnerability assessment of coastal natural hazards,state of Pará, Brazil 总被引:1,自引:0,他引:1
Studies carried out in the NE coastal zone of the State of Pará (Brazil) have recorded, in the last 25 years, numerous evidence
of natural impacts of the flood and erosion processes. As a consequence, diverse strategies and measures of population adaptation
have been implemented but with limited success. Therefore, in order to subsidize the Coastal Zone Management Program of Pará,
this paper aims to identify, assess and classify natural and socio-economic vulnerabilities of this coastal zone by means
of a Geographical Information Systems (GIS)-based composite coastal vulnerability index (CVI). In spite of the data problems
and shortcomings, using ESRI’s Arcview 3.2 program, the CVI score, to classify, weight and combine a number of 16 separate
natural and socio-economic variables to create a single indicator provides a reliable measure of differences (5 classes) among
regions and communities that are exposed to similar ranges of hazards. The results are presented in three maps referred to
as Natural, Socioeconomic and Total Vulnerability. The confidence associated with the results obtained, the need to utilize
another variables, and to frequently update the ones used already were analyzed and discussed. 相似文献
926.
927.
Johan Nelson 《Behavioral ecology and sociobiology》1995,37(4):217-223
Theory on microtine mating systems predicts that male spacing behavior will be related to female spatial and temporal distribution. However, data from a natural population of field voles, Microtus agrestis, indicated a potential influence of female density on the spacing behavior of males. Therefore, I experimentally investigated the relative importance of female density and female spatial distribution for the spacing behavior of males in M. agrestis. Males were radio-tracked in enclosed natural habitats in which females at different densities were placed in two different spatial arrangements: clumped versus even distribution. Female density was the main factor determining male spacing behavior. At the high female density males had smaller home ranges and moved shorter distances between radio-tracking recordings. Also, home ranges were more exclusive at high female density. However, since there was a significant positive correlation between home range size and range overlap, range exclusiveness seemed to be influenced by female density indirectly through the effect of range size. Female spatial distribution, on the other hand, had no influence on male home range exclusiveness. 相似文献
928.
Integration of Flow and Chemical Sensing for Guidance of Autonomous Marine Robots in Turbulent Flows
We explored the utility of odor-gated rheotaxis (OGR) with a biomimetic robot. OGR is a widely accepted biological plume-tracing strategy that uses mean flow and chemical detection for guidance. In experiments which contrasted the `classic' single-sensor formulation of the strategy against one which used two sensors and against another which combined the use of two sensors and memory of past stimulation patterns we quantified the relative advantages of each. The use of two, spatially separated, chemical sensors confers a significant advantage and still greater performance is obtained with rudimentary memory. The performance of the American lobster under the same turbulent dispersal regime leads us to conclude that significantly more effective plume tracing strategies remain to be discovered. 相似文献
929.
Altered responses to female odors in parasitized male mice: neuromodulatory mechanisms and relations to female choice 总被引:5,自引:0,他引:5
M. Kavaliers D. D. Colwell K.-P. Ossenkopp T. S. Perrot-Sinal 《Behavioral ecology and sociobiology》1997,40(6):373-384
There is accumulating evidence that females may preferentially select parasite-free or -resistant males. Minimal attention
has, however, been paid to the mate preferences and responses of the parasitized male hosts themselves. Here, we considered
the effects of parasitic infection on male host mate responses, the neuromodulatory correlates of these responses, and the
relations of these responses to female mate choice. Using an odor “preference” test, we examined the effects of different
stages of an acute, sub-clinical infection with the naturally occurring, enteric, single host, protozoan parasite, Eimeria vermiformis, on the responses of male mice, Mus musculus domesticus, to the odors of estrous females along with the responses of uninfected females to the parasitized males. At 4 days post-infection
(non-infective, pre-patent stage) E. vermiformis-infected male mice showed a significantly decreased preference for the odors of estrous females, whereas at 10 days post-infection
(infective, patent stage) infected males showed a significantly increased preference for the odors of estrous females. Parasitized
males displayed no significant changes in their responses to the odors of non-estrous females, supporting effects on the reproductively
related responses of the host. In parallel, estrous females displayed a reduced interest in the odors of infected males. Least
interest was expressed in the odors of the patent, infective males, consistent with the avoidance of contagion. Using selective
opioid peptide receptor agonists and antagonists we found evidence that enhanced kappa opioid peptide (e.g., dynorphin) activity
was related to the decreased sexual interest of the pre-infective males, while augmented delta opioid peptide (e.g., enkephalin)
activity was associated with the enhanced responses of the infective males to females. We further showed that acute kappa
opiate administration reduced the responses of uninfected males to females and that uninfected females displayed modified
responses to the odors of uninfected males subject to acute modifications of opioid activity. We suggest that these differential
shifts in endogenous opioid activity in the parasitized males are associated with and, or related to alterations in neuro-immune
and endocrine functions. These findings show that parasitic infection can have, depending on the stage of infection and associated
neuromodulatory changes, either significant facilitatory or inhibitory effects on male host preferences for and responses
to females.
Received: 22 April 1996 / Accepted after revision: 15 March 1997 相似文献
930.
Parasitic wasps orient to green leaf volatiles 总被引:12,自引:0,他引:12
Summary Undamaged plants emit low levels of green leaf volatiles (GLVs), while caterpillar-damaged and artificially damaged plants emit relatively higher levels of certain GLVs. Female braconid parasitoids,Microplitis croceipes, oriented to both damaged plants and to individual GLVs in no-choice tests in a wind tunnel, but seldom oriented to undamaged plants. Female ichneumonid parasitoids,Netelia heroica, also oriented to individual GLVs in a wind tunnel. Males of both wasp species failed to orient to the GLVs. These data show that leaf-feeding caterpillars can cause the release of GLVs, and that parasitic wasps can respond to these odors by flying upwind (chemoanemotactic response), which brings the wasps to their caterpillar hosts. This supports the hypothesis that plants communicate with members of the third trophic level,i.e., plants under herbivore attack emit chemical signals that guide natural enemies of herbivores to sites of plant damage. In this interaction, the GLVs serve as tritrophic plant-to-parasitoid synomones. That parasitoids from two different wasp families oriented to GLVs suggests that the response may be widespread among the Hymenoptera.Mention of a commercial or proprietary product does not constitute an endorsement by the U.S. Department of Agriculture 相似文献